Studies are proposed to investigate the relationships between gonadal hormones, the brain and behavior. The primary problem to be studied is the nature and biological basis for the excitatory and inhibitory effects of progesterone in the control of female receptivity. We plan to establish the neural sites of action for these effects and to test whether these effects are mediated by protein synthesis. A second set of studies will be concerned with the sexual differentiation process. We will study whether the differential binding of estrogen to hypothalamic nuclei which is found in males and females is a result of early hormonal stimulation and is involved in the control of behavior. The hormone levels of neonates will be manipulated and their behavior and neural response to estrogen will be studied in adulthood. A third line of research will consist of studies of the hormonal control of proceptive or stimulus seeking behavior in female animals. These studies will test the hypothesis that proceptive and receptive behaviors are under differential hormonal control.